Yes. You still need to clean and flux it for reuse, and you may need to bang it on a hard surface while hot to remove excess solder so the new pipe can fit inside, but yes, unless it is split or otherwise defective, it is reusable.

It does take a little time and effort to get the old solder cleaned off so the fitting will fit over the pipe, so you might want to consider if saving a few cents is worth it. Even a seemly small amount of solder will prevent the pieces from slipping together. Other than that, there is nothing wrong with reusing fittings.

Do you feel that there are no compatibility concerns between older and newer solder?

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No.
The new lead free mixes well with 50/50 and a new coating of flux
The lead free makes a much better joint.
I'm able to "break" an old 50/50 joint by twisting the fitting.
That would never happen with a Leadfree joint.

Ah, but you can't beat the flow of 50/50 with quicker wetting out as the solder heats up, and quicker setup as the solder cools.

If you plumb for art* rather than drinking from, then it's the solder of choice.

* Plumbing for art involves soldering together dry plumbing systems for the fun of it but never actually collecting them to a potable water supply for use. Not many people do it but a few of us solder joints for the thrill, normally at the weekends. Enjoying plumbing is what distinguishes DIY'ers from paid professionals.